1. Field of the Invention
The present invention relates to an image coding apparatus and an image coding method for coding an image signal of a Bayer array.
2. Description of the Related Art
A CCD or CMOS image sensor is used in an image pickup element of a recent digital camera. In this case, in an image pickup element of a single plate type, for example, by receiving object light through a color filter of a Bayer array as illustrated in FIG. 7, pixel data of green, blue, and red (hereinbelow, called RAW data) is obtained. In the example of FIG. 7, the color filter is constructed by a periodic layout pattern of G0 (green), R (red), B (blue), and G1 (green). Since a human visual sensitivity is more sensitive to a brightness component than that to a color component, an area which is twice as large as that for red or blue is allocated to green containing a large quantity of brightness component. Since the RAW data of the Bayer array has only information of one color component to one pixel, it is necessary to generate three color components of green, blue, and red to one pixel. Such a process for generating such three color components as mentioned above is called a de-mosaicking process. Generally, when image data is recorded, image data of an RGB signal obtained by the de-mosaicking process or image data obtained by transforming the RGB signal into a YUV signal is coded and recorded. However, since the image data obtained by the de-mosaicking process has a data amount which is thrice as large as that of the RAW data, there is such a problem that it takes a time for a coding processing, or the like. Therefore, a method whereby the RAW data before the de-mosaicking process is coded and recorded has also been proposed. For example, a method whereby the RAW data of the Bayer array is arranged in a tetragonal lattice manner for every color component and is coded by using MPEG-2 (ISO/IEC 13818-2) or MPEG-4 AVC (ISO/IEC 14496-10) is shown (for example, refer to the Official Gazette of Japanese Patent Application Laid-Open No. 2011-166219).
However, in the RAW data of the Bayer array, since pixel data of the green component has an information amount which is twice as large as that of the blue component or red component and an amount of coding processing to the green component is twice as large as that of the blue or red component, a method of more efficiently coding the image data of the green component is demanded.